The present invention relates to a method and a device for characterizing at least one element for storing energy via capacitive effect.
The fie d of the invention is the field of determining a characterizing indicator for energy storing means via capacitive effect, and more particularly the field of electrochemical energy storing means via capacitive effect, and even more particularly the field of the energy storage means commonly called supercapacitors or ultracapacitors.
It had been thought that an electrochemical energy storing element via capacitive effect in theory physically behaves like a perfect capacitor of capacitance C. But experience has shown that many interference phenomena arise within the electrochemical element. Experience has also shown that the single really significant interference effect at the usage ranges of the storage element is the loss of energy by the joule effect. This phenomenon is modelled by adding in an equivalent series resistance (ESR) in series with the perfect capacitor of capacitance C.
For optimum safe operation of an application using one or more electrochemical energy storing elements vie capacitive effect, it is important to be aware of the indicators characterizing each storage element, such as the amount of energy stored by each storage element, also called state of charge (SOC) or a state of health (SOH) of each storage element.
Determining these indicators for each storage element depends on many intrinsic parameters, the most significant of which are the values for C and ESR. These different values each depend on other physical parameters such as pressure, temperature, etc. and on the changes in the storage element over time.
However, determining the values for C and ESR requires that the operational fluctuations of the storage element are taken into account.
Thus, in order to obtain the operational indicators of a storage element, the current methods and devices determine the values for C and ESR over specific ranges of operation, in which the storage element has a “perfectly” predictable behaviour; ranges that are difficult to produce or have a random character in standard operation. This is why the current methods and devices regularly apply specific procedures of the controlled current transition type +I/−I or −I/O for measuring ESR and the controlled charge or discharge type at constant current I for measuring C.
However, in most applications, these procedures are difficult to envisage/apply while the application using the storage element is in operation, such as for example a motor vehicle application. Moreover, these procedures do not allow measurements to be obtained in real time and under real conditions, i.e. in situ.
As a result, the current methods and devices do not make it possible to characterize a capacitive storage element in situ, under real operating conditions without having to stop the application using the storage element, regardless of the application using the storage element.